fix: grammar and punctuation marks! (#11073)

* fix: grammer

Fix punctuation and grammar for better readability.

* Update docs/tutorial/part-eight/index.md

Great!

Co-Authored-By: amandeepmittal <[email protected]>

Author: amandeepmittal

docs/tutorial/part-eight/index.md

@@ -25,7 +25,7 @@ Lighthouse is included in Chrome DevTools. Running its audit -- and then address
 
 Let's try it out!
 
-First you need to create a production build of your Gatsby site. The Gatsby development server is optimized for making development fast; But the site that it generates, while closely resembling a production version of the site, isn't as optimized.
+First, you need to create a production build of your Gatsby site. The Gatsby development server is optimized for making development fast; But the site that it generates, while closely resembling a production version of the site, isn't as optimized.
 
 ### ✋ Create a production build
 
@@ -73,7 +73,7 @@ Inclusion of a web app manifest is one of the three generally accepted [baseline
 
 Quoting [Google](https://developers.google.com/web/fundamentals/web-app-manifest/):
 
-> The web app manifest is a simple JSON file that tells the browser about your web application and how it should behave when 'installed' on the users mobile device or desktop.
+> The web app manifest is a simple JSON file that tells the browser about your web application and how it should behave when 'installed' on the user's mobile device or desktop.
 
 [Gatsby's manifest plugin](/packages/gatsby-plugin-manifest/) configures Gatsby to create a `manifest.webmanifest` file on every site build.